1. Field of the Invention
The present invention relates to a 3-dimensional image processing method, 3-dimensional image processing device, and 3-dimensional image processing system, and particularly relates to 3-dimensional image processing method, 3-dimensional image processing device, and 3-dimensional image processing system, wherein information of specular reflection is obtained without fail even when photographing objects with extremely narrow angle ranges of specular reflection.
2. Description of the Related Art
In the event of reproducing a real object as a 3-dimensional image using computer graphics, there is a technique used wherein images taken of the real object with a camera are applied to each portion of the real object being 3-dimensionally reproduced. With such a technique, multiple images taken from multiple directions are prepared so that the 3-dimensional image can be observed from various viewpoints, and images suitable for the viewpoints are selected at the time of reproduction, and applied to each portion of the shape of the 3-dimensionally reproduced real object.
However, there is a problem with this technique, in that reproduction can be made only regarding the illumination state used at the time of inputting data from the real object, and reproduction cannot be made under an illumination state which is different to that at the time of photography. Also, camera images already contain shadows and highlights, so further applying shadows and highlights to objects to which camera images have been applied results in an unnatural-appearing image.
Now, SIGRAPH Computer Graphics Proceedings, Annual Conference Seriec, 1997, pp. 379–387, “Object Shape and Reflectance Modeling from Observation” describes the following technique. At the time of inputting data from a real object, the surface attributes, which are change in the manner of reflection observed on the surface of each of the parts of the real object due to the direction of illumination and the direction of observation (photography), are represented as a BRDF (Bi-directional Reflectance Distribution Function) and thus held, so in the event that an illumination state is arbitrarily set at the time of reproducing the 3-dimensional image, a 3-dimensional image can be observed as if the real object had been placed under the arbitrarily set illumination state. Also, a technique has been proposed wherein predetermined reflection model functions are introduced as BRDF, so as to represent the surface attributes by a reflection constant substituted into the reflection model function.
With this technique, a predetermined reflection model function serving as a BRDF is applied to the reflection properties of each part of the real object obtained by photographing the real object, and the reflection properties of each part of the real object are represented by the reflection constant within the reflection model function, and thus held. At the time of reproducing the 3-dimensional image, observation conditions such as arbitrary illumination conditions, the line of sight, and so forth, are set, and reflections occurring at each of the parts of the real object under those conditions are computed from the held reflection constant and reflection model function, thereby enabling shadows and highlights which are natural under the set observation conditions to be realized.
Also, for the above-described reflection model function, a reflection model function wherein the reflection of light is taken to be a linear sum of scattered (diffuse) reflection components and specular reflection components and wherein the state of the surface can be expressed by multiple reflection constants each, is used. The Phong reflection model is a representative example of such.
However, in the event of reproducing 3-dimensional images by holding data of the real object in such a technique, there is the need to use a light source which can approximate point light sources and parallel (infinite-distance) light sources as the illumination light source for inputting data from the real object, due to the properties of the BRDF. The reason is that since the BRDF is a function which describes what sort of reflection light the surface of the real object creates upon incidence of illumination light at a constant incident angle, prediction becomes extremely difficult when using image data taken of a real object illuminated with an illumination light of which light source position cannot be determined.
In the event of using such a light source, specular reflection may not be observed in the photographed image data with real objects in the case of real objects with metal glossiness or the like wherein the specular reflection only occurs at an extremely narrow angle range, resulting in erroneous information with no specular reflection being input. In order to avoid this, photography of the image needs to be carried out at angle intervals smaller than the expansion of the specular reflection, but this in itself is a problem, since this greatly increases the amount of image data to be processed and troublesome photography tasks.